The present invention is generally related to magnetic sensors. The present invention is also related to anisotropic magneto-resistance (AMR) sensors. The present invention is also related to sensors utilized in automotive applications. Additionally, the present invention is related to magnetoresistors utilized in magnetic sensor devices.
Magnetoresistors are often utilized for the contactless detection of changes in state, such as the measurement of an angular position of a rotatably mounted part. Magnetoresistive-based sensors typically include magnetic field-dependent resistors, which are arranged in a bridge circuit configuration and through which a control current is fed. When a magnetoresistive-based sensor is influenced by a magnetic field, a voltage can be established in which the magnitude of the voltage depends on the magnitude and direction of the magnetic field associated with the sensor.
The relationship between an associated bridge circuit voltage and the magnetic field direction can be utilized in a contactless AMR (Anisotropic Magneto Resistive) sensor, for example, to detect the angular position of a rotatably mounted part. Such sensors are particularly useful in automotive applications. If precise measurement is to be possible at all, a zero point must first be defined, or a calibration of the sensor must be performed. AMR sensors are typically configured from an AMR film that is formed from a magnetic substance that exhibits a magnetoresistive effect and generally possesses a single-layered structure.
A magneto-resistive sensor (e.g., AMR sensor) may be acted upon by a magnetic field oriented in a particular manner, such that a definite control current can be applied to the current contacts of an associated bridge circuit. The voltage that is then established at the other contacts can be measured on an ongoing basis. In general, the serpentine pattern of magnetoresistive material utilized in magnetic sensors such as AMR sensors can be connected electrically in a Wheatstone bridge arrangement in order to sense changes in the resistance of the magnetoresistive material in response to changes in the strength of a magnetic field component in the plane of the magnetoresistive elements. In order to monitor the changes in the resistance of the material, associated components, such as amplifiers, are generally connected together to form an electrical circuit, which provides an output signal that is representative of the strength of the magnetic field in the plane of the sensing elements. When the circuit is provided on a silicon substrate, electrical connections between associated components can be made above the surface of the silicon or by appropriately doped regions beneath the components and within the body of the silicon substrate. Components can be connected to each other above the surface of the silicon by disposing conductive material to form electrically conductive paths between the components. When appropriately doped regions within the silicon substrate connect components in electrical communication with each other, an electrically conductive path can be formed by diffusing a region of the silicon with an appropriate impurity, such as phosphorous, arsenic or boron to form electrically conductive connections between the components.
An AMR sensor can be processed with the aid of a laser until such time as the offset voltage, when no magnetic field is applied, becomes equal to zero. Such magneto-resistive sensors are thus ideally suited for angular position applications and for use as angular position sensors. AMR sensors and magnetoresistor-based devices are thus well known in the art. An example of a magnetic sensor configuration is depicted in U.S. Pat. No. 5,667,879, xe2x80x9cTaN/NiFe/TaN an isotropic magnetic sensor element,xe2x80x9d to Michael J. Haji-Sheikh, which is incorporated herein by reference. U.S. Pat. No. 5,667,879 discloses a stack of two refractory nitride layers and a magnetoresistive layer used to facilitate electrical connection between components of a sensor. The stack of tantalum nitride and nickel iron layers are disposed over a silicide layer that is, in turn, disposed on a diffusion of conductive material within the body of a silicon layer. A titanium tungsten layer is disposed on the stack and below a subsequent layer of a conductive metal such as aluminum. A silicon nitride passivation layer is disposed over all of the other layers.
AMR films associated with AMR sensors fundamentally respond differently to what is referred to in the art as an xe2x80x9ceasyxe2x80x9d axis and a xe2x80x9chardxe2x80x9d axis. An AMR sensor, which essentially senses a cross axis field, does not possess any basic hysteresis effect and will exhibit a maximum change in resistance as high 2% to 4%. These types of sensors are commonly utilized in a variety of sensing applications, including automotive applications thereof. It has been demonstrated in the art that a resistor (i.e., magnetoresistor) that is actuated with a field along the easy axis will experience a slight increase in resistance and that the same resistor actuated against the easy axis vector has a marked decrease in resistance (e.g., up to 1.2%), until the resistor reaches its desired switching field.
When the switching field is attained, the change in resistance may rise to a slightly positive change in resistance. This change in the switching field is associated with magnetization reversal. The phenomenon of magnetization reversal has been observed for years in ferromagnetic material. This effect has been considered a nuisance to be designed around. The present inventors have discovered, however, that this phenomenon can actually be utilized in a manner that offers advantages for magnetic sensing capabilities thereof. The invention described herein takes advantage of this phenomenon and discloses a unique method for achieving magnetic sensing capabilities thereof.
The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention and is not intended to be a full description. A full appreciation of the various aspects of the invention can be gained by taking the entire specification, claims, drawings, and abstract as a whole.
It is, therefore, one aspect of the present invention to provide an improved magnetic sensor.
It is another aspect of the present invention to provide an improved AMR sensor.
It is an additional aspect of the present invention to provide a method and system for detecting a magnetic field utilizing a magnetoresistor associated with a magnetic sensor.
It is yet another aspect of the present invention is to provide a method and system for detecting a magnetic field using the ability of the internal magnetization permalloy to reverse direction.
The above and other aspects of the invention can be achieved as is now described. A method and system for detecting a magnetic field utilizing a magnetoresistor of a magnetic sensor are described herein. A magnetoresistance associated with the magnetoresistor can be calculated such that the magnetoresistor comprises an initial magnetization direction thereof. The magnetic field is generally permitted to exceed an ability of the magnetoresistor to remain pointed in the initial magnetization direction, thereby enabling the magnetoresistor to experience a magnetization reversal thereof. The normalized resistance can be placed into a new state in response to the magnetization reversal thereof, thereby permitting the normalized resistance to be utilized as a switch thereof and allowing the magnetic sensor to detect changes in the magnetic field associated with the magnetoresistor.
The normalized resistance is generally altered in response to a change in the magnetic field. The magnetic field generally comprises a one-dimensional zero crossing magnetic field. Additionally, a switching field is associated with the magnetization reversal thereof. The magnetic field associated with the magnetoresistor also comprises a sinusoidally varying field. The sinusoidally varying field can be converted into a pulse train, such that a value of the switching field, which produces the pulse train thereof, is dependent on a geometry of the magnetoresistor.
A differential Wheatstone bridge circuit can be associated with the magnetic sensor, such that the differential Wheatstone bridge circuit produces an output in the form of a pulse train. The differential Wheatstone bridge includes one or more comparators and one or more D-flip-flop circuits, which together can generate a digital representation of the magnetic field. The magnetic field itself can be expressed as a one-dimensional zero crossing magnetic field. The magnetic sensor is generally configured as a permalloy sensor, including an AMR sensor. The normalized resistance is thus utilized as a switch until identifying a change in the normalized resistance.
The novel features of the present invention will become apparent to those of skill in the art upon examination of the following detailed description of the invention or can be learned by practice of the present invention. It should be understood, however, that the detailed description of the invention and the specific examples presented, while indicating certain embodiments of the present invention, are provided for illustration purposes only because various changes and modifications within the scope of the invention will become apparent to those of skill in the art from the detailed description of the invention and claims that follow.